1. Field of the Invention
The invention relates to methods of dyeing corespun yarn having an inorganic fiber core, and to dyed corespun yarns which can be formed by the inventive methods. The dyed corespun yarns of the invention are uniform in color and have a high strength retention. They have particular applicability in the formation of fabrics for applications such as upholstery, mattress and pillow ticking, bed spreads, pillow covers, draperies or cubicle curtains, wallcoverings, window treatments and clothing.
2. Description of the Related Art
The formation of single and multi-corespun yarns in the textile industry is known. Such yarns have particular applicability in the formation of fabrics for applications such as upholstery, mattress and pillow ticking, bed spreads, pillow covers, draperies or cubicle curtains, wallcoverings, window treatments and clothing. FIG. 1 illustrates a known double corespun yarn 100 which is conventionally produced on an air jet spinning apparatus. Such an apparatus is commercially available, for example, from Murata of America, Inc. and Feherer AG, and is described in the literature. See, e.g., U.S. Pat. Nos. 5,540,980, 4,718,225, 4,551,887 and 4,497,167, the entire contents of which patents are incorporated herein by reference. The basic structure of the yarn 100 includes a multi-filament core 102 of a first material surrounded by a first sheath 104 of a second material, and a second sheath 106 of a third material surrounding the first sheath 104.
After fabrication of the yarn, a dyeing process is carried out to impart desired color characteristics to the yarn. Conventional dyeing processes include prescour, dyeing and washing off clear sequences. Applicants have discovered that the conventional dyeing process can result in problems which adversely affect coloration and strength characteristics of corespun yarns which contain an inorganic fiber core. The coloration problem resulting from a conventional dyeing process commonly called xe2x80x9cgrin-through,xe2x80x9d and is particularly noticeable for medium and deep color shades. Grin-through is observed when the filament core or portion thereof and/or the first sheath or inner sheath fibers appear as undyed areas and/or loops 108 which are visible on the surface of the yarn product. This undesired effect renders the yarn less suitable or unsuitable for high quality fabrics requiring consistent, uniformly dyed yarns. The problem is especially aggravated when trying to achieve medium to deep shade yarn colors which contrast heavily against light colored, undyed core filaments, for example, white glass filaments and/or undyed portions of the first sheath or inner sheath fibers. The dyed corespun yarns resulting from conventional dyeing processes can also have significantly reduced strength when compared with the undyed (greige) yarns. Losses of original greige yarn strength of about 50% have been observed, when utilizing conventional yarn dyeing processes and techniques.
Through the invention, the inventors have discovered that subjecting the corespun yarn to significant thermal stress or shock during the conventional dyeing process is likely to cause both poor coloration and low strength characteristics of the yarn. For example, in the conventional disperse process, the yarn is typically exposed to temperatures at or above the boiling point of water. After contact with the yarn for a desired period, the temperature of the dye liquor may be rapidly decreased, for example, at a rate of about greater than 10xc2x0 F./min. The liquor is then drained from the system and then immediately followed with a cold water rinsing step. These steps of rapid cooldown/dropbath/cool rinse, can occur up to three times in the conventional dyeing process where prescour and reduction clear sequences are performed in addition to the dyeing sequence.
When the yarn is subjected to the conventional dyeing process, the differential shrinkage forces between the various fibers and filaments included in the yarn product can cause grin-through. The thermal stresses to which the yarn is subjected during the conventional dyeing process, particularly that due to rapid cooling of the yarn, can cause microcracking and microfracturing of the filaments making up the core 102. This is particularly problematic for yarns containing inorganic filament cores such as ceramic or glass cores. As a result of this microcracking and microfracturing, color uniformity and the filaments"" ability to impart strength to the dyed yarn and ultimately in the final woven fabric product are significantly reduced.
To overcome or conspicuously ameliorate the disadvantages of the related art, it is an object of the present invention to provide a novel method of dyeing a corespun yarn which comprises an inorganic fiber core and at least a first sheath. The method comprises: (a) contacting the corespun yarn with a dye liquor; (b) heating the dye liquor to a dyeing temperature for a time effective to dye the yarn; (c) cooling the dye liquor at a controlled rate; and (d) rinsing the yarn with water or with a mixture comprising the dye liquor and water. The dyed corespun yarn has a strength retention of about 80% or more based on the undyed yarn. The methods in accordance with the invention allow for the formation of uniformly dyed, high strength corespun yarns. The dyed yarns exhibit substantially no xe2x80x9cgrin throughxe2x80x9d and little to no yarn strength loss after dyeing. The dyed yarns in accordance with the invention have a typical strength retention, as measured by ASTM D2256, of 80% or more, preferably 90% or more, and more preferably 95% or more.
In a particularly preferred aspect of the invention, the corespun yarn is a fire resistant corespun yarn. The fire resistant corespun yarn comprises, for example, a core of a high temperature resistant continuous filament comprising fiberglass, a first sheath of blended staple fibers surrounding the core, the fibers comprising modacrylic fibers and melamine fibers, and a second sheath of staple fibers surrounding the first corespun yarn.
It is a further object of the invention to provide dyed, corespun yarns made by the inventive methods.
It is a further object of the invention to provide a dyed, corespun yarn comprising an inorganic fiber core. The dyed, corespun yarn has a strength retention of about 80% or more compared with the undyed yarn.
It is a further object of the invention to provide a dyed, corespun yarn comprising an inorganic fiber core and at least a first sheath. The dyed, corespun yarn exhibits substantially no grin-through.
In accordance with yet another aspect of the invention, a fabric is provided. The fabric includes a substrate which comprises the dyed corespun yarn.
In accordance with yet another aspect of the invention, a product upholstered with the fabric is provided.